Poorly written perl code that allows an attacker to specify the count to perl's 'x' string repeat operator can already cause a memory exhaustion denial-of-service attack.
A flaw in versions of perl before 5.15.5 can escalate that into a heap buffer overrun; coupled with versions of glibc before 2.16,
it possibly allows the execution of arbitrary code.

A regression has been fixed that was introduced in 5.14,
in /i regular expression matching,
in which a match improperly fails if the pattern is in UTF-8,
the target string is not,
and a Latin-1 character precedes a character in the string that should match the pattern.
[perl #101710]

In case-insensitive regular expression pattern matching,
no longer on UTF-8 encoded strings does the scan for the start of match only look at the first possible position.
This caused matches such as "f\x{FB00}" =~ /ff/i to fail.

The sitecustomize support was made relocatableinc aware,
so that -Dusesitecustomize and -Duserelocatableinc may be used together.

The smartmatch operator (~~) was changed so that the right-hand side takes precedence during Any ~~ Object operations.

A bug has been fixed in the tainting support,
in which an index() operation on a tainted constant would cause all other constants to become tainted.
[perl #64804]

A regression has been fixed that was introduced in perl 5.12,
whereby tainting errors were not correctly propagated through die().
[perl #111654]

A regression has been fixed that was introduced in perl 5.14,
in which /[[:lower:]]/i and /[[:upper:]]/i no longer matched the opposite case.
[perl #101970]

The list above is almost certainly incomplete as it is automatically generated from version control history.
In particular,
it does not include the names of the (very much appreciated) contributors who reported issues to the Perl bug tracker.

Many of the changes included in this version originated in the CPAN modules included in Perl's core.
We're grateful to the entire CPAN community for helping Perl to flourish.

For a more complete list of all of Perl's historical contributors,
please see the AUTHORS file in the Perl source distribution.

If you find what you think is a bug,
you might check the articles recently posted to the comp.lang.perl.misc newsgroup and the perl bug database at http://rt.perl.org/perlbug/ .
There may also be information at http://www.perl.org/ ,
the Perl Home Page.

If you believe you have an unreported bug,
please run the perlbug program included with your release.
Be sure to trim your bug down to a tiny but sufficient test case.
Your bug report,
along with the output of perl -V,
will be sent off to perlbug@perl.org to be analysed by the Perl porting team.

If the bug you are reporting has security implications,
which make it inappropriate to send to a publicly archived mailing list,
then please send it to perl5-security-report@perl.org.
This points to a closed subscription unarchived mailing list,
which includes all the core committers,
who be able to help assess the impact of issues,
figure out a resolution,
and help co-ordinate the release of patches to mitigate or fix the problem across all platforms on which Perl is supported.
Please only use this address for security issues in the Perl core,
not for modules independently distributed on CPAN.